This application is entitled to the benefit of French Patent Application No. 01.12534 filed on Sep. 28, 2001 in the name of Danfoss Maneurop S. A.
The subject of the present invention is a low-pressure gas circuit for a compressor, for example for a scroll-type compressor.
A scroll-type compressor of the type to which the invention relates comprises a sealed outer casing inside which is arranged a gas compression stage, mounted on a body, comprising a fixed scroll element and a moving scroll element, the moving element being driven by a motor in an orbital motion. The motor is mounted in an inner casing arranged concentrically inside the outer casing. The outer casing has a gas intake opening and with the inner casing and the element having the fixed scroll delimits a low-pressure zone. Oil for lubricating the upper bearing leaves via openings made in the body. As is known per se, the gas drawn into the compression stage passes through the motor to cool the latter.
A compressor needs to protected against the harmful effects of the return of liquid from the plant, whether this be refrigerant in the liquid state or oil. For this purpose, certain compressors are equipped with a deflector at the gas intake orifice formed in the outer casing.
Furthermore, the gas taken in by the compressor passes in contact with the oil leaving via the openings formed in the body. This results in mixing which is not always homogenous, and which can vary between two pockets of gas taken into the compression stage.
The purpose of the invention is to provide a device for circulating gas in the low-pressure zone of the compressor which protects the latter against the transients which may bring in liquid phases returning via the intake duct, which controls the circulation of oil by separating the streams of gas and of oil or liquid, which creates no pressure drops between the connection and the reserve of oil so as not to affect the oil balancing circuit for connection in parallel, particularly with compressors of different sizes, and which reduces the noise level by filtering out the compression noises (pulsation) originating from the compression stage.
The compressor to which it relates comprises, a sealed outer casing, inside which is arranged a gas compression stage driven by a motor; the motor is arranged inside the outer casing, and is fixed under the compression stage and connected in its lower part to a sealed lower casing which may comprise a guide element for allowing the motor shaft to rotate. The outer casing has a gas inlet opening and delimiting, with the assembly consisting of the body, the motor, the lower casing and the compression system, a low-pressure zone. The compressor being of the type in which the lubricating oil used to lubricate the compression system leaves via at least one opening made in the body, and in which the gas taken into the compression stage passes through the motor to cool it.
According to the invention, the lower part of the lower casing containing the motor is sealingly closed by a bottom, and at least one chimney is arranged in the annular space formed between the outer casing and the lower casing, this chimney being arranged substantially vertically along the motor and the lower casing. The chimney communicates in its upper part with the low-pressure zone of the compressor and, in its lower part, with the inside of the lower casing. One or more openings are made between the chimney and the bottom of the motor.
The gas arriving via the intake orifice at the low-pressure zone of the compressor is directed into the upper part of the ring-shaped space so as to separate the liquid phase returning via the intake circuit. As the lower part of the motor casing and the lower bearing of the compressor form a sealed space, the gas drops down from the upper part towards the bottom of the motor by means of one or more chimneys. Then it enters the lower casing to pass through the motor and cool it before reaching the compression stage.
According to a first embodiment, the compressor, includes a sealed outer casing, inside which is arranged a gas compression stage driven by a motor, the motor delimiting an inner casing the upper part of which forms a cavity for supplying the compression stage with gas and the lower part of which forms a gas inlet cavity at the bottom of the motor, the flow of gas between the lower cavity and the upper cavity being intended to cool the motor, the outer casing comprising a gas inlet opening and delimiting, with the inner casing and the body of the compression stage, a low-pressure zone. The compressor is of the type in which the oil lubricating the upper bearing(s) and/or thrust bearing(s) leaves via at least one opening formed in the body, is characterized in that the lower part of the inner casing is sealingly closed by a bottom, and at least one chimney is arranged in the annular space formed between the outer casing and the inner casing. The chimney is arranged substantially vertically along the inner casing, and communicates in its upper part with the low-pressure zone of the compressor and in its lower part with the inside of the inner casing.
According to another embodiment, the compressor includes a sealed outer casing inside which is arranged a gas compression stage, is characterized in that the body comprises a part in the form of a tubular skirt facing downwards and to the lower end of which the motor is fixed, this skirt delimiting with the motor a cavity for supplying the compression stage with gas. The lower bearing comprises a part in the form of a tubular skirt facing upwards extending as far as the motor and delimiting therewith a lower gas inlet cavity at the bottom of the motor, the gas passing from this lower cavity towards the upper cavity, cooling the motor. The lower part of the lower casing is delimited by the skirt and the lower bearing being closed by a sealed bottom, at least one chimney being arranged substantially vertically along the skirt, the motor and the skirt, inside the outer casing, this chimney communicating in its upper part with the low-pressure zone of the compressor and in its lower part with the inside of the cavity delimited by the skirt.
The chimney communicates in its upper part with the low-pressure zone of the compressor at a location not subjected to the presence of oil.
The use of one or more chimneys allows the liquid and gaseous phases to be separated during the upwards phase of the fluid from the intake orifice towards the entry to the chimney or chimneys.
That allows the oil returning from the low-pressure circuit to be separated out and makes it possible to make sure that the control, generated by the compressor, of the circulation of oil is not connected with the amount of oil returning in sudden bursts from the circuit, as, for example, is the case when a siphon is used on the low-pressure circuit.
Depending on the origin of operation, particularly in the phases of start-up, defrosting cycle or when there is a sudden demand, there is foaming and the amount of oil in circulation increases instantaneously and takes a fairly long time to stabilize the equilibrium value.
Because, in the device according to the invention, the gas flow circuit does not cross the stream of the oil leaving the upper bearing, it does not therefore become laden with oil.
According to one feature of the invention, each chimney is angularly offset with respect to the openings of the body allowing oil to return to the reservoir delimited by the bottom of the outer casing.
It is possible to envisage orientating a chimney in the sector of 0 to 170xc2x0 with respect to the plane passing through the axis of the compressor and the intake connection.
The use of at least two chimneys makes it possible to avoid the gas stream becoming laden with oil if the oil return is opposite the intake connection and between the two chimneys furthest from this connection.
According to one feature of the invention, the bottom which closes the lower casing containing the motor has at least one hole for discharging liquid to the reservoir delimited by the bottom of the outer casing.
This discharge hole allows drainage from inside the motor, avoiding, amongst other things, the washing of the lower bearing and/or of its thrust bearing as refrigerant for example migrates.
Advantageously, at least one opening made in the body and acting as a passage for the oil is extended downwards by a duct opening below the level of the intake opening of each chimney.
This arrangement avoids the constraint of orientating the chimneys with respect to the position of the openings made in the body and which are intended for the return of oil to the bottom of the outer casing. Depending on the position chosen, the length of each duct will need to vary according to its proximity to an inlet connection.
According to one embodiment of this compressor, each chimney consists of a profiled plate made of metal or synthetic material, fixed to the inner casing and delimiting a chimney with its outer surface.
The fixing may for example be afforded by screwing, using screws which serve to fix the upper and lower bearings to the motor casing.
According to another form of embodiment, each chimney consists of a profiled plate bearing, on the one hand, against the outer casing and, on the other hand, against the inner casing and delimiting a chimney therewith.
According to yet another embodiment, each chimney consists of a duct fixed to the inner casing.
In order to improve the uniformity of the gas flow rate through the motor, this compressor comprises, inside the inner casing and facing at least one opening for the conveying of gas by a chimney, a deflector for distributing the gas in the inner casing.
According to one option, each chimney is delimited on the outer casing side by a wall which has a central and longitudinal recess in which a duct for returning oil leaving the body to the oil reservoir delimited by the bottom of the outer casing is engaged on at least one chimney.
Advantageously, and so as to reduce the compression noises originating from the compression mechanism, in certain frequency ranges, at least one chimney comprises a baffle consisting, for example, of a plate or of a boss protruding inwards.
Introducing a bypass between the cavity of the low-pressure zone and locating the motor output in the upper part of the motor will make it possible to reduce pressure drops and, by the same token, to improve the efficiency of the machine.
According to another feature of the invention, the compressor comprises a chimney in the form of an annular duct enveloping the compressor drive system and placing the gases drawn in from the upper low-pressure zone of the compressor in communication with the opening or openings allowing the flow of gas to reach the lower part of the motor.
According to another feature of the invention, the compressor comprises at least one gas bypass duct between the low-pressure zone and the zone supplying the compression stage with gas.
According to another feature of the invention, the compressor comprises at least one duct for the bypassing of the gases of the low-pressure zone and the upper part of the motor.
According to a first embodiment of the invention, the compressor comprises a compression system having a moving scroll and a fixed scroll the relative motion of which is of the orbital type.
According to another embodiment of the invention, the compressor comprises a compression system which has two moving scrolls rotating about offset and parallel axes, and the relative motion of which is of the orbital type.
According to another embodiment of the invention, the compressor comprises a reciprocating-piston-type compression system.
According to yet another embodiment of the invention, the compressor comprises a rolling-piston-type compression system.